The Thermal Mechanical Fatigue (TMF) Analysis for an Exhaust Manifold An Application of File Based Coupling

Transcription

1 The Thermal Mechanical Fatigue (TMF) Analysis for an Exhaust Manifold An Application of File Based Coupling Shao-Chin Fan Engine Design Division HAITEC / CEC

2 CONTENTS INTRODUCTION WORK FLOW BOUNDARY CONDITIONS GAS SIDE COOLANT SIDE HEAT TRANSFER STEADY STATE TRANSIENT RESULT CONCLUSIONS 2

3 INTRODUCTION With stringent emission and fuel economic regulation, downsizing and upgraded performance will be the recent trend in IC engine design. Higher performance will introduce high exhaust temperature in exhaust system, which was designed to withstand high temperature, big vibration and stress from leakage-proof seal of tightened-bolt. A thermal with mechanical coupling analysis was applied in exhaust system to predict initiated cracks of exhaust manifold. 3

4 WORK FLOW Preparing Boundary Conditions 1D Cycle simulation B.C. for CFD CFD (STAR-CCM+) Exhaust system CFD (STAR-CCM+) Water jacket Temperature & HTC (STAR-CCM+) Mapping Thermal shock pattern FEM (Abaqus) Transient heat transfer FEM (Abaqus) Thermal Structure Anaylsis Coolant Speed Load 4

5 DESIGN SCENARIO Coolant Speed Load Full Load Motored Idle 215 sec 345 sec 495 sec Thermal shock pattern 5

6 BOUNDARY CONDITIONS Gas side boundary conditions: 1D cycle simulation to calculate full load, motored and idle boundary conditions for CFD model. The 1D cycle simulation model was verified with test data. 3D CFD simulation to calculate temperature and HTC (heat transfer coefficient) of ports, exhaust manifold, turbo and catalyst. Pressure (Pa) Pressure CRANKANGLE (deg) Temperature (K) Temperature CRANKANGLE (deg) Outlet Wall: constant temperature Inlet MassFlow (kg/s) Mass Flow CRANKANGLE (deg) Temperature (K) Temperature CRANKANGLE (deg) 6

7 BOUNDARY CONDITIONS Coolant side boundary conditions: 3D CFD to calculate temperature and HTC of cylinder head. The boundary conditions are test data. Pressure outlet Wall: constant temperature Mass flow rate inlet Mass flow rate 7

8 Mesh and Physics models Polyhedral mesh 765,363 cells Gradients Ideal gas Implicit unsteady K-Epsilon turbulence Multi-Component gas Non-reacting Realizable K-Epsilon two-layer Reynolds-Averaged Navier-Stokes Segregated flow Segregated fluid temperature Segregated species Three dimensional Turbulent Two-Layer all y+ wall treatment Polyhedral mesh 729,533 cells Gradients Constant density K-Epsilon turbulence Liquid Realizable K-Epsilon two-layer Reynolds-Averaged Navier-Stokes Segregated flow Segregated fluid temperature Steady Three dimensional Turbulent Two-Layer all y+ wall treatment 8

9 TRANSIENT RESULT Temperature distribution on the wall of exhaust manifold 9

10 BOUNDARY CONDITIONS Data Mapping: Import structure model and define the surface map data. Local Heat Transfer Coefficient and Local Heat Transfer Reference Temperature were mapped to structure model surfaces. The gas side CFD calculations are transient, only averaged 1 engine cycle data will be exported. 1 engine cycle = 720 deg crank angle 10

11 BOUNDARY CONDITIONS Gas side: The averaged Local Heat Transfer Coefficient and Local Heat Transfer Reference Temperature were mapped to FEM model. Heat Transfer Coefficient Temperature 11

12 BOUNDARY CONDITIONS Coolant side: The Local Heat Transfer Coefficient and Local Heat Transfer Reference Temperature were mapped to FEM model. Heat Transfer Coefficient Temperature 12

13 HEAT TRANSFER Steady state heat transfer results Steady state Full Load Motored Idle 13

14 HEAT TRANSFER Steady state heat transfer results Steady state vs. transient Full load: due to thermal inertia, areas with higher wall thickness are in the transient analysis cooler in comparison to the temperatures calculated in steady state analysis. Motored/Idle: due to thermal inertia opposite effect occur. Full Load Motored Idle Steady state Steady state Steady state Transient 2 nd cycle Transient 2 nd cycle Transient 2 nd cycle 14

15 TRANSIENT ANIMATION 15

16 STRUCTURE RESULTS Areas with equivalent plastic strain range ΔPEEQ Locations with highest equivalent plastic strain range are concentrated in the area of the flange towards the turbocharger. These locations show very good correlation with hardware test bed results. 16

17 DESIGN OPTIMIZATION Increase the transition radius as much as possible. Increase transition radius from dividing wall and reshape the ports in order to achieve bigger radius. Reduce this saddle shaped region (make it almost flat) in order to reduce the stress concentration. 17

18 CONCLUSIONS The work flow coupling with 1D cycle simulation, 3D CFD and FEM analysis is a reliable method to predict the thermal stress of exhaust manifolds. STAR-CCM+ can calculate accurate temperature boundary conditions for structure FEM model. Designer can modify the critical locations of the exhaust manifold base on the simulation results. And verify the new design by simulation without prototype and test cost. 18

19 Thank you! 19